Stu Miley (Brendan Fraser) has a successful and happy life. He is a cartoonist who draws the character Monkeybone. Stu is also in love with Julie McElroy (Bridget Fonda). He plans to marry her, but on the night he is going to propose, his alter-ego Monkeybone seems to intervene. Monkeybone is as raunchy as Stu is serious. It is as if the struggle within Stu overcomes him. As Stu and Julie are driving, an inflatable Monkeybone toy in the back seat suddenly blows up and hits Stu in the head. Stu crashes the car and ends up in a coma. Julie stays by his side. As a doctor whose specialty is sleep, she is convinced Stu's coma is nothing more than a deep state of sleep from which he will recover. In the mean time, Stu's coma takes him into an animated world where Monkeybone is causing havoc, trying to keep Stu from waking because Monkeybone doesn't want Stu to settle down and become a boring married man. Julie can try to help him at his bedside, but it is Stu who must overcome his alter-ego to return to Julie.